An artificial medium in which both an effective relative dielectric constant and an effective relative magnetic permeability are negative, what is called a “left-handed system medium” is a substance having a negative refractive index that does not exist in the natural world and shows a unique phenomenon in which a property of a wave motion is inverted to that of an ordinary substance, what is called a “right-handed system medium”. For instance, the inverted phenomenon includes a symbol (a negative refractive index) of an angle of refraction in the Snell's law, a direction of wave number vector (backward wave), the Doppler effect or the like. As an expansion of this conception, a matched zero refractive index medium in which both the effective relative dielectric constant and the effective relative magnetic permeability are zero also attracts a high attention. Thus, in various fields, studies are made for producing various kinds of highly developed devices and instruments by using characteristics of the left-handed system medium. For instance, in an optical field, studies are made for realizing a high resolution exceeding a diffraction limit for a lens by using the artificial medium. Further, in a field of microwave and millimeter-wave, studies are made for miniaturizing an antenna or achieving a high performance of an antenna by using the artificial medium.
It is known that a technique for forming the artificial left-handed system medium is roughly classified into two kinds. One of them is a technique using a transmission line and, for instance, non-patent literature 1 may be exemplified.
In this technique, an already established transmission theory and a right-handed system line realized by the theory are expanded in quality and a discrete inductor and a capacitor are inserted into the line to realize a left-handed system line. A great feature of this technique is to essentially show wide band characteristics. This technique is applied to an antenna supposed to be connected to a circuit element such as a filter or the transmission line and operates to an electromagnetic wave transmitted in space. Therefore, in this technique, it is extremely difficult to apply the transmission line type left-handed system medium to, for instance, a lens.
As compared therewith, as the left-handed system medium that can operate to the electromagnetic wave transmitted in the space, non-patent literature 2 may be exemplified.
This left-handed system medium has a structure having a split ring resonator combined with a conductor strip. Accordingly, the left-handed system medium has a restriction in principle that a conductor surface of the split ring resonator needs to be formed in parallel with the transmitting direction of an electromagnetic wave. As a result, the left-handed system medium has a demerit that production processes are extremely complicated.
As a structure of the left-handed system medium that can solve the above-described demerit and operate to the electromagnetic wave in the space, non-patent literature 3 may be exemplified. In this technique, the same patterns made of net shaped conductors are respectively arranged on front and back surfaces of a dielectric to realize the left-handed system medium.
Non-patent literature 1: C. Caloz And T. Itoh, “Novel microwave devices and structures based on transmission line approach of meta-materials” IEEE-MTT Int'l Symp., vol. 1 pp. 195-198, June 2003
Non-patent literature 2: R. A. Shelby, D. R. Smith, S. Schultz, “Experimental Verification of a Negative index of Refraction”, Science 292, pp. 77-79 2001
Non-patent literature 3: Gunnar Dolling, Christian Enkrich, Martin Wegner, Costas M. Soukoulis, Stefan Linden, OPTICS LETTERS, Vol. 31, No. 12, 2006